1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to a method of rasterizing image data printed on an address space associated with an intermediate transfer member.
2. Description of the Related Art
Ink jet printers typically use one or more monochrome or color printheads to produce a printed document. In typical inkjet printers, the carrier moves horizontally across the print medium and the print medium is indexed in an, advance direction independently between scans of the carrier. This motion allows typical inkjet printers to print using an orthogonal, rectilinear address space. That is, all addressable pixels are located on a rectangular grid with an orthogonal axis. Inkjet printers print on the print medium using a desired ink dot density, such as a 600xc3x97600 dots per inch (dpi) grid. This process produces a printed document of high quality; however, often the time associated with printing is undesirably long. Non-printing time occurs during which the printheads are mechanically moved without jetting ink. This waste of mechanical energy in turn leads to unnecessary delays before an image is placed on the print medium and delivered to the user.
In order to minimize the non-printing time in an ink jet printer, it is known to use an intermediate transfer member (ITM), wherein an image is printed onto a repeating surface, such as a cylinder, and transferred to a print medium in a subsequent operation. The use an ITM to print upon minimizes the time and mechanical energy wasted during non-printing operations and provides a known, controlled and repeatable surface upon which to form the image. During the printing operation, the ITM rotates at a fixed speed. At the same time, the carrier moves from one end of the ITM to the other end at a constant linear speed as to follow a helical path on the ITM. The entire imaging operation is performed with no stops or starts with either the carrier system or the ITM system, thus minimizing energy waste. Therefore, it is no longer possible to produce or use an orthogonal, square, rectangular address space with the printheads during printing.
A continuous ITM as described above is also used with laser printers. A laser beam typically is reflected from a rotating polygon mirror and traversed across a photoconductive ITM as the polygon rotates. This occurs very fast and thus the helical effect associated with each line of pixels is negligible.
Ink jetting printers may also include an ink jet cartridge having a printhead with multiple or redundant major columns of ink jetting orifices. Each major column typically consists of multiple, staggered columns of ink jetting orifices, with the major columns being spaced apart from and parallel to each other. By providing redundant major columns of ink jetting orifices, each including multiple staggered columns of ink jetting orifices, print artifacts caused by clogged nozzles, faulty circuitry or the like may be avoided.
What is needed in the art is a method of printing with an inkjet printer using a continuous ITM, wherein the helical effect associated with printing on the ITM is minimized.
The present invention provides a method of operating an ink jet printer wherein the image data is skewed to offset the helical effect caused by printing on an intermediate transfer member.
The invention comprises, in one form thereof, a method of operating an inkjet printer. An intermediate transfer member is movable in an advance direction. A carrier supports a printhead, and is movable relative to the intermediate transfer member in a direction generally perpendicular to the advance direction. The printhead defines a plurality of raster lines extending over the intermediate transfer member at a non-perpendicular, fixed angle vector relative to the advance direction. A bitmap image is defined which corresponds to an image to be formed on the intermediate transfer member. A bitmap image includes a plurality of rows and columns of pixels, with at least one image data corresponding to each pixel. The bitmap image is skewed such that the image data for at least one column within the bitmap image is shifted a predetermined number of pixel locations, dependent upon the fixed angle vector.
The invention comprises, in another form thereof, a method of operating an ink jet printer. An intermediate transfer member is movable in an advance direction. A carrier supports a printhead, and is movable relative to the intermediate transfer member in a direction generally perpendicular to the advance direction. The printhead defines a plurality of raster lines extending over the intermediate transfer member at a non-perpendicular, fixed angle vector relative to the advance direction. A bitmap image is defined which includes an array of pixels. The bitmap image includes image data corresponding to each pixel. The bitmap image is skewed such that the image data for a selected pixel location is shifted to a different pixel location, dependent upon the fixed angle vector.
An advantage of the present invention is that the helical affect associated with printing on the continuous ITM is minimized.
Another advantage is that skewing of the image data to offset the helical affect may be selectively carried out depending on the quantitative value of the fixed angle vector.
Yet another advantage is that the spacing of the address space on the ITM and print medium may be varied by proportionally adjusting the linear carrier speed and rotational ITM speed.